Conventionally, microphones using an acoustic sensor called an ECM (Electret Condenser Microphone) as a compact microphone have been used. However, because the ECM is easily affected by heat and a microphone using an acoustic sensor manufactured using an MEMS (Micro Electro Mechanical Systems) technique (MEMS microphone) excels in terms of support for digitalization and downsizing, the MEMS microphones have been adopted in recent years (for example, see JP 2011-250170A).
JP 2011-250170A is an example of background art.